Abstract. The Mass Absorption Cross section (MAC) and Absorption Ångström
Exponent (AAE) have been commonly estimated for ambient aerosols but rarely
for black carbon (BC) or organic aerosol (OA) alone in the ambient
conditions. Here, we provide estimates of BC (and OA) MAC and AAE in East
Asian outflow, by analyzing field data collected at the Gosan ABC super
site. At this site, EC (and OC) carbon mass, the aerosol absorption
coefficient at 7 wavelengths and PM mass density were continuously measured
from October 2009 to June 2010.

We remove the absorption data with significant dust influence using the mass
ratio of PM10 to PM2.5. The remaining data shows an AAE of about
1.27, which we suggest represent the average carbonaceous aerosol (CA) AAE at
Gosan.

We find a positive correlation between the mass ratio of OC to EC and CA AAE,
and successfully increase the correlation by filtering out data associated
with weak absorption signal. After the filtering, absorption coefficient is
regressed on OC and EC mass densities. BC and OA MACs are found to be 5.1
(3.8–6.1) and 1.4 (0.8–2.0) m2 g−1 at 520 nm
respectively. From the estimated BC and OA MAC, we find that OA contributes
about 45% to CA absorption at 520 nm. BC AAE is found to be 0.7–1.0, and is probably even lower considering the instrument bias. OA AAE is
found to be 1.6–1.8. Compared with a previous estimate of OA MAC and
AAE near biomass burning, our estimates at Gosan strongly suggest that the
strongly-absorbing so-called brown carbon spheres are either unrelated to
biomass burning or absent near the emission source.